A conventional screw 1 is disclosed in FIG. 1 and generally includes a head 11 with a shank 12 connected there to which has threads 13 defined in an outer surface thereof. The thread includes several recesses 131 and a cutting edge 132 is formed between the adjacent recesses 131. When the screw 1 is threaded into an object 10, the cutting edges 132 of the threads 13 cut the fibers of the object such that the screw 1 can be easily merged into the object 10. It is noted that the threads 13 with smaller angle defined by the upper flank and the lower flank of the threads has sharper cutting edges so as to cut the fibers easily. Nevertheless, such threads cannot bear larger torque and could be damaged by larger torque. If the threads includes larger angle between the upper flank and the lower flank, the threads can bear larger torque but has less cutting feature. This makes the user to apply more force to drive the screw 1 into the deeper position of the object 10.
The present invention intends to provide a screw that includes two types of threads and the thread close to the point bear larger torque so as to be threaded into the object at the first stage without damaging the thread, and the other thread includes sharper cutting edges which make the screw easily to be sent into the object.